1. Field of the Invention
The present invention relates to a lens body tube which images an image light by a projection lens to thereby project an image on a screen and also relates to a projector having the lens body tube.
2. Description of the Related Art
A projector is provided with a lens body tube having a lens and a rotary cam tube for moving the lens in an optical axis direction. A lens frame of a ring or cylindrical shape is fixed to the lens (see a JP-A-2003-66316, for example). The lens frame is attached within the rotary cam tube so as to be movable freely. An elongated cam hole is formed at the outer periphery of the rotary cam tube. A lens roller to be inserted into the cam hole is attached to the outer periphery of the lens frame. A supporting tube for rotatably supporting the rotary cam tube is disposed within the rotary cam tube. A flange portion protruded radially is formed at the rear end portion of the supporting tube. The flange portion is fixed to a fixing member within the projector. The lens roller is inserted into the cam hole via an insertion hole formed at the supporting tube. When the rotary cam tube is rotated, the lens frame moves in the optical axis direction to thereby perform the zooming of a projection image.
The cam hole is formed at the rotary cam tube by the cutting process since the size management thereof is required strictly. On the other hand, the supporting tube is formed by the injection molding of resin so as to reduce the cost thereof.
In recent years, a projector arranged to have a large movable length of the lens frame has been proposed in order to increase a zoom value. In order to increase the movable length of the lens frame, it is necessary to also increase the length of each of the rotary cam tube and the supporting tube.
However, since the supporting tube is fixed to the fixing member at the flange portion of the rear end portion, when the length of each of the supporting tube becomes long, there arise a problem that the stability of the supporting tube degrades when being fixed. Thus, it is considered to dispose the supporting tube on the outside of the rotary cam tube and form the flange portion on the front side than the rear end portion of the supporting tube. In this case, a lever protruding in the outer periphery direction is attached to the rotary cam tube and a lever insertion hole for passing the lever therethrough is formed at the supporting tube, whereby when the lever is rotated from the outside of the supporting tube, the rotary cam tube rotates to perform the zooming operation.
However, in this case since the lever insertion hole is required to be formed to have a length within a rotary operation range (rotary angle range of the rotary cam tube) of the lever at the time of zooming, there arises problem that the intensity of the supporting tube degrades. Further, since the supporting tube is formed by the injection molding of resin, there arises a problem that the resin does not flow smoothly at the periphery of the lever insertion hole and the forming stability degrades and so the size thereof can not be managed strictly.